Title

Mechanisms by which 17β-Estradiol (E2) suppress neuronal cox-2 expression

Date of Award

12-1-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Field of Study

Biomedical Sciences

Department

Graduate School of Biomedical Sciences

First Advisor

Rosalie M. Uht

Second Advisor

Rebecca L. Cunningham

Third Advisor

Eric B. Gonzales

Abstract

Data from animal models indicate that 17β-estradiol (E2) deprivation increases susceptibility to neurodegenerative diseases. E2 attenuates inflammatory response by suppressing expression of pro-inflammatory genes; however, the mechanisms by which E2 suppress neuronal pro-inflammatory genes are not well established. Histological analyses of postmortem human brains suggest that neuronal cyclooxygenase-2 (COX-2) is upregulated in early stages of Alzheimer’s disease (AD) and in Parkinson’s disease (PD).

Given that COX-2 is selectively expressed in a subset of neurons in the hippocampus, cerebral cortex, and amygdala, we investigated mechanisms by which E2 could down-regulate cox-2 expression in a neuronal system. To characterize the effect of E2 on cox 2 in a neuronal system, we used the AR-5 and N27 rat neuronal cell line models. Our data indicate that E2 and ERβ agonist diarylpropionitrile (DPN) suppress COX-2 pre-mRNA and mRNA levels to the same extent in AR-5 but not in N27. Furthermore, PHTPP, a selective ERβ antagonist, reversed the effect of both E2 and DPN in AR-5.

Because the cox-2 promoter lacks palindromic estrogen response elements (EREs), we targeted a proximal promoter region with a nuclear factor- ĸB (NF-ĸB) response element implicated in cox-2 regulation. E2 and DPN failed to increase ERβ occupancy at the cox-2 promoter. Rather, DPN decreased promoter occupancy of p65 NF-κB subunit and acetylation of histone 4 (Ac-H4). Treatment with the non-specific HDAC inhibitor Trichostatin A (TSA) counteracted DPN’s repressive effects on cox-2 expression.

In keeping with the effect of TSA, E2 and DPN increase HDAC1 promoter occupancy; however recruitment of HDAC3 was unchanged. HDAC1 is known to form a complex with Swi-independent A (Sin3A); E2 and DPN increased Sin3A occupancy. The recruitment of HDAC1 seems to correlate with decreased acetylation of histone 4 (H4) and not histone 3 (H3). Furthermore E2 alone increased methylation status in the cox-2 proximal promoter. Taken together, these data suggest that E2 suppresses neuronal cox-2 expression through ERβ-mediated recruitment of HDAC1, Sin3A and a concomitant reduction of p65 and H4 levels.

Here we conclude that E2 suppresses neuronal cox-2 expression through a mechanism that involves a combination of decreasing activator and increasing repressor recruitment to the cox-2 promoter.

Comments

Winfred Stacey, Mechanisms by which 17β-Estradiol (E2) suppress neuronal cox-2 expression. Doctor of Philosophy (Biomedical Sciences), September 2015. 101 pages, 32 titles, 16 illustrations. Available December 2016.

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